#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
int main()
{
	double sum = 0;
	int i = 0;
	for(i = 1;i <= 100;i++)
	{
		if(0 == i%2 )
		{
			sum = sum - 1.0/i;
		}
		else if(1 == i%2)
		{
			sum = sum + 1.0/i;
		}
	}
	printf("%lf\n",sum);
	return 0;
}